1. Basics of Heat Transfer
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This document discusses the three main modes of heat transfer: conduction, convection, and radiation. Conduction occurs through direct contact within solids and liquids at rest, transferring energy from high to low temperature particles. Convection involves fluid motion, either forced or natural, transferring energy between a surface and fluid with different temperatures. Radiation transfers energy through electromagnetic waves in a vacuum or medium. It provides the Fourier law of heat conduction and discusses heat transfer by conduction in a slab. It also explains Newton's law of cooling for convection and the Stefan-Boltzmann law for radiation heat transfer between black surfaces. The document lists common materials and their thermal conductivities and concludes with details about a heat transfer textbook
1. Basics of Heat Transfer
- 2. 2 Heat and Mass Transfer Module 1 Conduction Heat Transfer Module 2 Convection Heat Transfer Module 3 Boiling and Condensation Module 4 Heat Exchanger Module 5 Radiation Heat Transfer Module 6 Mass Transfer
- 3. 3 Heat transfer – A Practical approach Y. A. Cengel Fundamental of Heat and Mass transfer Incropera and Dewitt Heat transfer - A Basic approach Osizik Heat Transfer A. Bejan Heat Transfer A. J.P. Holman
- 4. Thermodynamics does not answer the following questions. 1. How does the heat transfer take place? 2. What is the rate of heat transfer? 3. How long the heat transfer process will continue? Modes of heat transfer 1. Conduction heat transfer 2. Convection heat transfer 3. Radiation heat transfer 4
- 6. Conduction heat transfer Conduction is the mode of heat transfer in which heat is transferred from the high temperature region to low temperature region in solids and liquid at rest. The energy is transferred from high energy particles to low energy particles of the medium due to interaction between them. 6
- 7. 7 Fourier law of heat conduction 2 W/mfluxHeat WferHeat trans dx dT k A Q q dx dT kAQ Where k – thermal conductivity of the material W/mK A – Area normal to heat transfer direction m2 dT/dx - temperature gradient in the direction of heat flow K/m
- 8. L X=0 X=L L TTk A Q q L TT k A Q q L TT dx dT 21 12 12 8 Heat conduction in a slab T1 T2
- 9. Material Thermal Conductivity W/mK Aluminium 204.2 Copper 386 Zirconium 22.7 Glass wool 0.0372 Card board 0.064 Water 0.5978 Brass 111 Carbon steel 54 Lead 35 Saw dust 0.059 Asbestos-cement board 0.74 9
- 10. Convection heat transfer Convection heat transfer occurs between the fluid in motion and the bounding surface when there is temperature difference exists between them. Forced convection heat transfer the fluid flow is assisted by a fan or pump. Free or natural convection heat transfer, the flow of the fluid induced by the buoyancy forces which arise from the density difference caused by the temperature variation within the fluid. 10 The convection heat transfer is classified into two types:
- 11. Newton’s law of cooling retemperatuFluid-T retemperatuSurface-T tcoefficienferheat trans-hwhere W/mfluxHeat s 2 TTh A Q q s The value of heat transfer coefficient depends on the type of flow, the geometry of the body and flow passage area, physical properties of the fluid, the average temperature and the mechanism of heat transfer. 11
- 12. Radiation heat transfer Radiation is the mode of heat transfer in which the heat may also be transferred in perfect vacuum. Maxwell’s electromagnetic wave theory Planck’s quantum theory 4 ATQ Stefan-Boltzman law Radiation heat exchange between two black surfaces 4 2 4 1112 TTAFQ 12
- 13. Reflection Spot • What are the three modes of heat transfer? • Write the Fourier law of heat conduction. • Higher the thermal conductivity of material heat conduction will be high. (True/False) • What are the two types of convection heat transfer? • Heat transfer coefficient in forced convection is ………….(more/less) than free convection • Radiation mode does not require a medium for heat transfer. (Yes/No) 13
- 14. Features of the book Lucid explanation of subject content More solved problems from Anna University Question Papers Two mark questions with answers Publisher Anuradha Publications Chennai 14
- 15. Dr. K. Kannan Professor Mechanical Engineering Anjalai Ammal Mahalingam Engineering College Kovilvenni – Tamil Nadu [email protected] 15